Engine Knocking....

[Alan]

Not heard that one before but could it be something like a broken valve spring.

[Colin Wilks]

Assuming this is not the noise you hear when the engine is running, my first thought was the starting handle spring is catching and releasing as you rotate it, and if so is entirely separate to the main problem!

[Denis Sweeney]

Engine is now out of the car head, block and sump removed, haven’t removed the front conical section so cannot comment on the condition of smaller timing gear.
Very heavy carbon deposits and lots oil everywhere.

[Denis Sweeney]

Following on from my last post on this topic, please see the attached PDF file for the latest update.
As always comments always welcome
Cheers Denis S

[dickie65]

Hi.
Try Meths to remove red hermatite.
Piston to head clearance can be reduced by carbon build up.
You can usually see piston shaped marks in the carbon on the head if that is the case. No signs in your pictures though.
Carbon getting hot can cause pre ignition Knocking noises.

[Dave Wortley]

The noise in your video where you are turning the engine over with the starting handle sounds normal to me and is one valve/spring/tappet assembly being released of load when it comes off the top of the cam and the camshaft is momentarily lightly loaded before the load is reapplied on the next assembly.

[John Cornforth]

Hi Denis

I have read your pdf with interest, I guess you are frustrated that there hasn't been an "Ah Ha" moment and nothing is obviously wrong. As I previously mentioned, my engine is also a 2 bearing with a HC head. It sounds a bit generally harsh but this smooths out when its properly warmed up and is only really apparent around 1900 to 2400 RPM when the throttle is more than about 2/3rds open. I too have 4 thou end float on the camshaft. I attribute the harshness ( I wouldn't describe it as knocking) to general wear in the path from crank to distributor (3 gear pairs), causing timing scatter.

The oil and carbon looks like my engine did the last time it was apart. In my case I suspect this was partly oil coming past the rings because the bores were glazed, maybe due to incorrect running in technique on my part. The other factor is the choice of plugs, in road use these engines seem more inclined to run cool rather than hot. If the plug tips don't get got enough then they can cause a slight misfire and exacerbate the carbon deposit problem. I found a change to a "hotter/softer" plug helped, I run (genuine) NGK B6HS but some people go to a B5HS type which is one step hotter.

Re-reading this long thread, did you ever definitely establish whether your noise was load/throttle related or only RPM related ? It makes a big difference to the potential causes. Even the propshaft turns at engine RPM in top gear.

[Denis Sweeney]

Thanks for the comment John, the original noise came on under load in third and fourth, revving the engine whilst stationary nothing was evident.
Later it started to sound just generally rough, a member of the local A7OC came for a spin to try to diagnose the issue. Nothing conclusive was detected but he said it sounded pretty rough and so that’s when I decided to stop driving her and investigate.
You are not the first to suggest a “hotter” plug to assist in reducing carbon deposits.
I do not know what the acceptable limits on piston clearances are but I did read +0.003 on bore to piston diameter for pistons up to 2.5” this was from a Pitman’s book. But not sure if this was for new build or maximum wear??

[Reckless Rat]

Late 37 head on my RP - I run B5HS plugs. Clean as a whistle. They would never falter even before I had the engine rebored and it was burning oil quicker than a Deltic on full chat.

Not sure that the hotter plugs will reduce carbon build up, that's usually down to engine wear but they will resist oiling up better.

[Graham Barker]

Hi Denis, for my own benefit, I was hoping that you would have had more learned responses to your detailed description of your engine condition so that I could gather some ideas regarding similar conditions of my Ruby engine. I have sent you a pm. 
Regards, Graham.